"[H]e was situated in a wheelchair holding an unknown object...It's tight quarters in there, and he was able to corner the officer back into the corner of the room," said Silva.

Officer Matthew Marin, a five-year vet, feared for his partner's life and fired the fatal shots, police said.

The case will be reviewed by HPD homicide, internal affairs and a Harris County Grand Jury.

Update: HPD gives its official version of events:

Officers responded to a disturbance at the above residence, the Healing Hands Assisted Home Care, a residence for mentally challenged persons. When officers arrived, they encountered the suspect, seated in a wheelchair. The suspect was agitated and began to yell at the officers and threatened to kill them and the other residents of the home.

As he yelled at the officers, he waved a shiny object in his hand in their direction. The suspect refused the officers' verbal commands to drop the object and advanced in a threatening manner toward one of the officers. As the suspect backed one of the officers into a corner, he attempted to stab the officer with the object. Officer Marin, fearing for his partner's life, and his own safety, discharged his duty weapon one time, striking the suspect. The object was discovered to be a shiny, ball point pen.

And HPD chief Charles A. McClelland, Jr. has issued a statement, something not usually done with every police shooting:

On Saturday, September 22, 2012, officers from the Houston Police Department responded to a call for service involving a disturbance with a violent person at 4309 Polk Street. During the response to the incident, an officer discharged his firearm resulting in the death of a citizen, Brian C. Claunch.

The Houston Police Department places the highest value on human life and events like these are tragic and unfortunate for everyone involved. All Houston Police Officers receive mandatory crisis intervention training specifically dealing with persons experiencing mental crisis. As we do in all instances of this nature, the Houston Police Department's Homicide and Internal Affairs Divisions, and the Harris County District Attorneys Office, Civil Rights Division, are investigating this incident.

In addition, I have also asked the local office of the Federal Bureau of Investigation (FBI) to monitor and investigate this incident. As I have done throughout my tenure as Police Chief, to the extent I can, the Houston Police Department will be open and transparent in all aspects of our response to this tragic event.

It is my desire to have everyone reserve judgment until all the facts and evidence in this investigation have been gathered.